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Cutting a flap on the surface of your eye and vapourizing patches of your cornea using ultraviolet light may sound like a bad idea, but millions of people worldwide have done just that — undergone laser eye surgery — in an effort to correct their vision.

So how does laser eye surgery actually work?

First, let’s talk about how vision works. Light reflects off the objects we see and passes through the outer layer of the eye, called the cornea, through to the pupil and lens, which focuses the light onto the retina at the back of the eye. The retina sends signals to the brain through the optic nerve, which then constructs images.

For clear vision, incoming light must bend (refract) so that it focuses (converges) at a single point on the retina. To focus light properly, the shape of the eye, cornea and lens are important.

Did you know?: If the eye is too long, light is focused in front of the retina, causing objects in the distance to appear blurry (near-sightedness). The opposite is true for seeing objects up close.

Permanently changing the shape of your cornea with laser eye surgery can improve vision by correcting the focus of incoming light. According to Health Canada, laser eye surgery is the most commonly practiced procedure to correct vision problems caused by refractive errors. During the surgery, a highly precise, computer-controlled laser device, usually an excimer laser, is used by eye surgeons to reshape the cornea. The laser produces a cool beam of ultraviolet light that vapourizes tiny amounts of eye tissue.

Did you know?: One pulse of an excimer laser removes 0.25 microns of tissue (one micron is one millionth of a metre). For comparison, human hair is about 70 microns thick and red blood cells are 8 microns in diameter.

In Canada, the two most-commonly performed types of excimer laser surgery are PRK (Photo-Refractive Keractectomy), and LASIK (Laser Assisted in situ Keratomileusis). During PRK, surgeons remove the outer layer of the cornea and then use the laser to reshape the tissue under the surface of the cornea. During LASIK, surgeons cut a flap in the cornea and lift it to reshape the tissue below. Patients’ eyes generally heal faster after a LASIK procedure, although it is a bit more complicated than PRK.

Both procedures are usually fast, safe and painless and, for the most part, are permanent. Although, there’s no guarantee your vision will be perfect after surgery and a small percentage of people experience side effects. Risks range from dry eyes and poor night vision to infection and corneal flap dislodgment. It’s important to talk with your eye doctor about the risks and benefits and if you’re under 18, you’ll have to wait a few years for your prescription to stabilize before you are able to have the surgery. On the bright side, that’s more time to save up, since LASIK can cost up to a few thousand dollars per eye!

Did you know?: LASER is an acronym for Light Amplification of Stimulated Emission of Radiation.

Learn More!

Information about LASIK and other types of laser eye surgery

Step-by-step graphic of the LASIK procedure

Information about how lasers work

Information about how the eye works

Information about vision and refractive errors





Krysta Levac

After an undergraduate degree at the University of Guelph, I earned a PhD in nutritional biochemistry from Cornell University in 2001. I spent 7 years as a post-doctoral fellow and research associate in stem cell biology at Robarts Research Institute at Western University in London, ON. I currently enjoy science writing, Let's Talk Science outreach, and volunteering at my son's school. I love sharing my passion for science with others, especially children and youth. I am also a bookworm, a yogi, a quilter, a Lego builder and an occasional "ninja spy" with my son.

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